1. Field of the Invention
The present invention relates to a polymerizable composition particularly used for a dental treatment.
2. Description of the Conventional Art
The present invention relates to a polymerizable composition used by mixing two kinds of pastes. More particularly, the present invention relates to the polymerizable composition that even though each of the pastes before polymerization is stored for a long period of time without being refrigerated, the polymerizable composition does not gelate and a curing time of the polymerizable composition does not change with time. Furthermore, the polymerizable time does not delay or quicken even though the polymerizable composition is stored.
A method of combining an organic peroxide and an aromatic tert-amine and using the mixture as a chemical polymerization catalyst has been conventionally used for mixing and polymerizing polymerizable compositions at ordinary temperature, where the polymerizable compositions include a monomer, an oligomer, and a prepolymer of acrylate, a methacrylate and the like which have radical polymerization property. This method can control a time of polymerization and can increase preservation stability of the composition before polymerization by adjusting an amount of the organic peroxide blended with a first paste and an amount of the aromatic tert-amine blending with a second paste, and together using a polymerization inhibitor. However, the polymerizable composition has a problem that a cured body after polymerization is discolored while time passes by the aromatic tert-amine. In addition, the organic peroxide is unstable. Thus, when a great amount of the organic peroxide blends with the paste of the polymerizable composition and the paste is stored for a long period of time, the paste tend to gelate before polymerization. By contrast, when a great amount of the polymerization inhibitor blends with the paste in order to secure long-term preservation stability, a polymerization time comes to be too long. Therefore, the conventional polymerizable composition should be refrigerated and stored for regulate the reaction of the organic peroxide.
As another chemical polymerization catalyst, a composition is obtained by combining an organic aromatic compound including at least one —SO2— group, a peroxide, and an aromatic tert-amine. However, since the organic peroxide and the aromatic tert-amine are used, there are still problems that a cured body discolors and preservation stability is low.
Further, a polymerization method using trialkylborane is also known. However, trialkylborane has a disadvantage that trialkylborane cannot previously blend with the polymerizable composition including a (meth)acrylate compound having radical polymerization property since trialkylborane is oxidized easier than aromatic tert-amine. Therefore, trialkylborane should be stored in a vessel separating from the (meth)acrylate compound, and should be added to the polymerizable composition at each use. Thus, an operation is complicated.
The present inventors developed before a composition including a ternary catalyst including a pyrimidinetrione derivative, an organohalogen compound, and an organometallic compound, and filed a patent application for this composition under Japanese Patent Application Laid-Open No. 2003-105008. Since this composition does not include amine, a cured body does not discolor, and the composition can be used under acid conditions. However, the ternary catalyst still has a problem in preservation stability of the pyrimidinetrione derivative.
In addition to this, for example, Japanese Patent Application Laid-Open No. 58-219281 discloses a combination of cumene hydroperoxide and a thiourea derivative. This combination has better stability to higher temperature than that of conventional ones. However, a polymerizable composition using the combination has a problem that a curing reaction generated by cumene hydroperoxide and a thiourea derivative is slow. Even if a blending concentration is sufficient, a polymerization speed which is appropriate for dental adhesives cannot be obtained.
In order to improve this composition, for example, Japanese Patent Application Laid-Open No. 2007-056020 discloses a combination of cumene hydroperoxide and N-acetylthiourea, which is obtained by a redox reaction under the existence of a copper compound. Since this combination has comparatively high thermal stability and does not include an aromatic tert-aimine, a cured body does not discolor with time. Further, this combination is characterized in that it is not influenced by acid of a (meth)acrylate compound having an acid group, which is conventionally blended in order to give adhesive property to a polymerizable composition. Thus, the composition has excellent preservation stability. However, when an operator adheres a dental prosthesis to a tooth, a dental material is required to have property that the material is cured suitably within a time desired by an operator, and to be constant in a curing time for every product. Any of the combinations mentioned above still does not satisfy the requirements of stability of the curing time.